When the Planets Align

Mercury, Venus and Jupiter gather in the glow of twilight

By J. Alex Knoll

As the sun sets, Jupiter, Venus and Mercury emerge in its wake. These three planets will spend the coming week in one another’s company, playing a celestial game of leap-frog low in the west-northwest after sunset.
While these planets appear just a few degrees from one another, they are actually hundreds of thousands of miles apart. All the planets, earth included, travel along the same plane — called the ecliptic — as they orbit the sun. Every so often two or more planets align as seen from our earth-bound vantage.
Thursday the 23rd, Mercury makes its first move, pulling within two degrees of Venus and then powering above and past its neighbor. Of the two, Venus, at nearly –4 magnitude, is far brighter than Mercury, which shines at magnitude –1, still equal to the brightest star. Jupiter, between the two in brightness, is roughly three degrees higher.
Come Friday, the three planets are just a few degrees from one another, so close that you can spot them together in binoculars and even some telescopes. Saturday evening they are at their closest, all within two and a half degrees of one another. Jupiter is the highest, to the upper left of Mercury, with Venus below. Sunday they form a tight, near-perfect triangle, but now it is Mercury marking the highest point. The triangle breaks Monday, as Mercury continues to scale the horizon, while Jupiter and Venus remain side by side only a couple degrees apart. By Tuesday night, Venus is just one degree to the upper right of Jupiter with Mercury a few degrees above the two.
Finally, Wednesday the 29th, all three planets align above the west-northwest horizon, all within five degrees of one another. Hereafter, Jupiter disappears amid the glare of the setting sun, Mercury dims and begins its descent toward the horizon, while Venus continues to climb higher night by night.